| 1 | /* |
| 2 | * This is a module which is used for rejecting packets. |
| 3 | */ |
| 4 | |
| 5 | /* (C) 1999-2001 Paul `Rusty' Russell |
| 6 | * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org> |
| 7 | * |
| 8 | * This program is free software; you can redistribute it and/or modify |
| 9 | * it under the terms of the GNU General Public License version 2 as |
| 10 | * published by the Free Software Foundation. |
| 11 | */ |
| 12 | |
| 13 | #include <linux/module.h> |
| 14 | #include <linux/skbuff.h> |
| 15 | #include <linux/ip.h> |
| 16 | #include <linux/udp.h> |
| 17 | #include <linux/icmp.h> |
| 18 | #include <net/icmp.h> |
| 19 | #include <net/ip.h> |
| 20 | #include <net/tcp.h> |
| 21 | #include <net/route.h> |
| 22 | #include <net/dst.h> |
| 23 | #include <linux/netfilter/x_tables.h> |
| 24 | #include <linux/netfilter_ipv4/ip_tables.h> |
| 25 | #include <linux/netfilter_ipv4/ipt_REJECT.h> |
| 26 | #ifdef CONFIG_BRIDGE_NETFILTER |
| 27 | #include <linux/netfilter_bridge.h> |
| 28 | #endif |
| 29 | |
| 30 | MODULE_LICENSE("GPL"); |
| 31 | MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>"); |
| 32 | MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv4"); |
| 33 | |
| 34 | /* Send RST reply */ |
| 35 | static void send_reset(struct sk_buff *oldskb, int hook) |
| 36 | { |
| 37 | struct sk_buff *nskb; |
| 38 | const struct iphdr *oiph; |
| 39 | struct iphdr *niph; |
| 40 | const struct tcphdr *oth; |
| 41 | struct tcphdr _otcph, *tcph; |
| 42 | unsigned int addr_type; |
| 43 | |
| 44 | /* IP header checks: fragment. */ |
| 45 | if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET)) |
| 46 | return; |
| 47 | |
| 48 | oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb), |
| 49 | sizeof(_otcph), &_otcph); |
| 50 | if (oth == NULL) |
| 51 | return; |
| 52 | |
| 53 | /* No RST for RST. */ |
| 54 | if (oth->rst) |
| 55 | return; |
| 56 | |
| 57 | /* Check checksum */ |
| 58 | if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP)) |
| 59 | return; |
| 60 | oiph = ip_hdr(oldskb); |
| 61 | |
| 62 | nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) + |
| 63 | LL_MAX_HEADER, GFP_ATOMIC); |
| 64 | if (!nskb) |
| 65 | return; |
| 66 | |
| 67 | skb_reserve(nskb, LL_MAX_HEADER); |
| 68 | |
| 69 | skb_reset_network_header(nskb); |
| 70 | niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr)); |
| 71 | niph->version = 4; |
| 72 | niph->ihl = sizeof(struct iphdr) / 4; |
| 73 | niph->tos = 0; |
| 74 | niph->id = 0; |
| 75 | niph->frag_off = htons(IP_DF); |
| 76 | niph->protocol = IPPROTO_TCP; |
| 77 | niph->check = 0; |
| 78 | niph->saddr = oiph->daddr; |
| 79 | niph->daddr = oiph->saddr; |
| 80 | |
| 81 | tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr)); |
| 82 | memset(tcph, 0, sizeof(*tcph)); |
| 83 | tcph->source = oth->dest; |
| 84 | tcph->dest = oth->source; |
| 85 | tcph->doff = sizeof(struct tcphdr) / 4; |
| 86 | |
| 87 | if (oth->ack) |
| 88 | tcph->seq = oth->ack_seq; |
| 89 | else { |
| 90 | tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin + |
| 91 | oldskb->len - ip_hdrlen(oldskb) - |
| 92 | (oth->doff << 2)); |
| 93 | tcph->ack = 1; |
| 94 | } |
| 95 | |
| 96 | tcph->rst = 1; |
| 97 | tcph->check = tcp_v4_check(sizeof(struct tcphdr), |
| 98 | niph->saddr, niph->daddr, |
| 99 | csum_partial(tcph, |
| 100 | sizeof(struct tcphdr), 0)); |
| 101 | |
| 102 | addr_type = RTN_UNSPEC; |
| 103 | if (hook != NF_INET_FORWARD |
| 104 | #ifdef CONFIG_BRIDGE_NETFILTER |
| 105 | || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED) |
| 106 | #endif |
| 107 | ) |
| 108 | addr_type = RTN_LOCAL; |
| 109 | |
| 110 | /* ip_route_me_harder expects skb->dst to be set */ |
| 111 | skb_dst_set(nskb, dst_clone(skb_dst(oldskb))); |
| 112 | |
| 113 | if (ip_route_me_harder(nskb, addr_type)) |
| 114 | goto free_nskb; |
| 115 | |
| 116 | niph->ttl = dst_metric(skb_dst(nskb), RTAX_HOPLIMIT); |
| 117 | nskb->ip_summed = CHECKSUM_NONE; |
| 118 | |
| 119 | /* "Never happens" */ |
| 120 | if (nskb->len > dst_mtu(skb_dst(nskb))) |
| 121 | goto free_nskb; |
| 122 | |
| 123 | nf_ct_attach(nskb, oldskb); |
| 124 | |
| 125 | ip_local_out(nskb); |
| 126 | return; |
| 127 | |
| 128 | free_nskb: |
| 129 | kfree_skb(nskb); |
| 130 | } |
| 131 | |
| 132 | static inline void send_unreach(struct sk_buff *skb_in, int code) |
| 133 | { |
| 134 | icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0); |
| 135 | } |
| 136 | |
| 137 | static unsigned int |
| 138 | reject_tg(struct sk_buff *skb, const struct xt_target_param *par) |
| 139 | { |
| 140 | const struct ipt_reject_info *reject = par->targinfo; |
| 141 | |
| 142 | /* WARNING: This code causes reentry within iptables. |
| 143 | This means that the iptables jump stack is now crap. We |
| 144 | must return an absolute verdict. --RR */ |
| 145 | switch (reject->with) { |
| 146 | case IPT_ICMP_NET_UNREACHABLE: |
| 147 | send_unreach(skb, ICMP_NET_UNREACH); |
| 148 | break; |
| 149 | case IPT_ICMP_HOST_UNREACHABLE: |
| 150 | send_unreach(skb, ICMP_HOST_UNREACH); |
| 151 | break; |
| 152 | case IPT_ICMP_PROT_UNREACHABLE: |
| 153 | send_unreach(skb, ICMP_PROT_UNREACH); |
| 154 | break; |
| 155 | case IPT_ICMP_PORT_UNREACHABLE: |
| 156 | send_unreach(skb, ICMP_PORT_UNREACH); |
| 157 | break; |
| 158 | case IPT_ICMP_NET_PROHIBITED: |
| 159 | send_unreach(skb, ICMP_NET_ANO); |
| 160 | break; |
| 161 | case IPT_ICMP_HOST_PROHIBITED: |
| 162 | send_unreach(skb, ICMP_HOST_ANO); |
| 163 | break; |
| 164 | case IPT_ICMP_ADMIN_PROHIBITED: |
| 165 | send_unreach(skb, ICMP_PKT_FILTERED); |
| 166 | break; |
| 167 | case IPT_TCP_RESET: |
| 168 | send_reset(skb, par->hooknum); |
| 169 | case IPT_ICMP_ECHOREPLY: |
| 170 | /* Doesn't happen. */ |
| 171 | break; |
| 172 | } |
| 173 | |
| 174 | return NF_DROP; |
| 175 | } |
| 176 | |
| 177 | static bool reject_tg_check(const struct xt_tgchk_param *par) |
| 178 | { |
| 179 | const struct ipt_reject_info *rejinfo = par->targinfo; |
| 180 | const struct ipt_entry *e = par->entryinfo; |
| 181 | |
| 182 | if (rejinfo->with == IPT_ICMP_ECHOREPLY) { |
| 183 | printk("ipt_REJECT: ECHOREPLY no longer supported.\n"); |
| 184 | return false; |
| 185 | } else if (rejinfo->with == IPT_TCP_RESET) { |
| 186 | /* Must specify that it's a TCP packet */ |
| 187 | if (e->ip.proto != IPPROTO_TCP |
| 188 | || (e->ip.invflags & XT_INV_PROTO)) { |
| 189 | printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n"); |
| 190 | return false; |
| 191 | } |
| 192 | } |
| 193 | return true; |
| 194 | } |
| 195 | |
| 196 | static struct xt_target reject_tg_reg __read_mostly = { |
| 197 | .name = "REJECT", |
| 198 | .family = NFPROTO_IPV4, |
| 199 | .target = reject_tg, |
| 200 | .targetsize = sizeof(struct ipt_reject_info), |
| 201 | .table = "filter", |
| 202 | .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) | |
| 203 | (1 << NF_INET_LOCAL_OUT), |
| 204 | .checkentry = reject_tg_check, |
| 205 | .me = THIS_MODULE, |
| 206 | }; |
| 207 | |
| 208 | static int __init reject_tg_init(void) |
| 209 | { |
| 210 | return xt_register_target(&reject_tg_reg); |
| 211 | } |
| 212 | |
| 213 | static void __exit reject_tg_exit(void) |
| 214 | { |
| 215 | xt_unregister_target(&reject_tg_reg); |
| 216 | } |
| 217 | |
| 218 | module_init(reject_tg_init); |
| 219 | module_exit(reject_tg_exit); |